Primary Age Related Tauopathy (Part) is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Primary Age-Related Tauopathy (PART) is a neuropathological entity characterized by the presence of Alzheimer-type neurofibrillary tangles (NFTs) composed of abnormal tau] protein] in the medial temporal lobe, occurring in the absence of significant [amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- ([Aβ[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- plaque pathology. First formally proposed as a distinct diagnostic category in 2014 by Crary et al.[1], PART represents one of the most common neuropathological findings in aging brains[1] and is now recognized as a major contributor to the spectrum of age-related cognitive changes 1(https://pubmed.ncbi.nlm.nih.gov/25348064/) (Crary et al., 2014).
PART challenges the traditional [amyloid cascade hypothesis] of [Alzheimer's disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX-- by demonstrating that significant tau pathology can develop independently of [amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- deposition. While its clinical significance continues to be debated, growing evidence indicates that PART can contribute to cognitive impairment[2], particularly when it occurs alongside other neurodegenerative co-pathologies such as [LATE[/diseases/[late[/diseases/[late[/diseases/[late--TEMP--/diseases)--FIX--, [Lewy body disease], and cerebrovascular disease 2(]https://pmc.ncbi.nlm.nih.gov/articles/PMC7849162/) (Neves et al., 2021).
¶ Historical Context and Nomenclature
Before the PART terminology was introduced, the phenomenon of neurofibrillary tangles without amyloid plaques was described under several overlapping terms, including:
- Tangle-only dementia (TOD): Coined by Yamada (2003), describing cases with significant tangle pathology and dementia but no plaques
- Tangle-predominant senile dementia (TPSD): Describing elderly individuals with abundant limbic tangles and variable cognitive impairment
- Neurofibrillary tangle-predominant dementia (NFTPD): A related concept focusing on dementia cases with disproportionate tangle burden
- Braak stage-only pathology: Cases classified by the Braak staging system for NFTs without corresponding CERAD plaque scores
The 2014 consensus paper by Crary and colleagues unified these concepts under the single term "PART," providing standardized diagnostic criteria and a framework for systematic investigation 1(https://pubmed.ncbi.nlm.nih.gov/25348064/). However, PART remains a subject of ongoing debate: some researchers view it as a distinct entity, while others consider it an early or incomplete form of [Alzheimer's disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX-- 3(https://link.springer.com/article/10.1007/s00401-025-02943-x).
The hallmark of PART is the presence of Alzheimer-type NFTs composed predominantly of both 3-repeat (3R) and 4-repeat (4R) tau isoforms, forming paired helical filaments (PHFs) identical to those seen in [Alzheimer's disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX--. The topographic distribution of tangles in PART follows a stereotypical pattern that mirrors the early Braak stages of AD:
- Braak stage I–II: NFTs confined to the transentorhinal and [entorhinal [cortex[/brain-regions/[cortex[/brain-regions/[cortex[/brain-regions/[cortex--TEMP--/brain-regions)--FIX--
- Braak stage III: NFTs extend to the [hippocampus[/brain-regions/[hippocampus[/brain-regions/[hippocampus[/brain-regions/[hippocampus--TEMP--/brain-regions)--FIX-- (CA1 sector) and amygdala
- Braak stage IV: More widespread hippocampal and temporal cortical involvement
By definition, PART encompasses cases with Braak stages 0–IV, though the majority of cases cluster at stages I–III. Cases reaching Braak stage IV remain a contentious "gray zone" where the distinction from early AD becomes difficult 1(https://pubmed.ncbi.nlm.nih.gov/25348064/).
The defining feature that separates PART from AD is the absence or minimal presence of [amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- plaques. Diagnostic criteria specify:
- Definite PART: Braak tangle stage I–IV with Thal amyloid phase 0 (no amyloid plaques)
- Possible PART: Braak tangle stage I–IV with Thal amyloid phase 1–2 (minimal amyloid deposition, which may represent age-related amyloid accumulation rather than true AD pathology)
Cases with Thal phase ≥3 are excluded from the PART diagnosis, as this level of amyloid deposition suggests transition to AD neuropathologic change 2(https://pmc.ncbi.nlm.nih.gov/articles/PMC7849162/).
- Ghost tangles: Extracellular remnants of dead [neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX-- that contained NFTs, commonly found in advanced PART
- Neuropil threads: [Tau[/entities/[tau-protein[/entities/[tau-protein[/entities/[tau-protein--TEMP--/entities)--FIX---positive neurites in the medial temporal lobe
- Granulovacuolar degeneration (GVD): Often accompanies PART in the [hippocampus[/brain-regions/[hippocampus[/brain-regions/[hippocampus[/brain-regions/[hippocampus--TEMP--/brain-regions)--FIX--
- Tau-positive [neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX-- in the locus coeruleus, [nucleus basalis of Meynert[/brain-regions/[nucleus-basalis-of-meynert[/brain-regions/[nucleus-basalis-of-meynert[/brain-regions/[nucleus-basalis-of-meynert--TEMP--/brain-regions)--FIX--, raphe nuclei, and olfactory bulb
¶ Epidemiology and Prevalence
PART is extraordinarily common in the aging population. Autopsy studies have reported the following prevalence estimates:
- Present in virtually all individuals over age 80[3] (Braak stage I or higher)
- Approximately 20–30% of cognitively normal elderly individuals[3] at autopsy meet criteria for definite PART
- PART is found even in younger adults: a 2020 study found PART pathology in 38% of autopsy cases under age 50[4] 4(https://pubmed.ncbi.nlm.nih.gov/33147361/)
- Higher Braak stages (III–IV) of PART are found in approximately 5–10% of autopsy series
Sex-based differences have been noted, with some studies reporting a slightly higher prevalence of advanced PART in women, mirroring the sex differences observed in AD tangle pathology. Unlike AD, PART shows no consistent association with [APOE[/genes/[apoe[/genes/[apoe[/genes/[apoe--TEMP--/genes)--FIX--.
The clinical significance of PART is amplified when it co-occurs with other neurodegenerative pathologies:
- LATE-NC ([Limbic-predominant Age-related [TDP-43[/entities/[tdp-43[/entities/[tdp-43[/entities/[tdp-43--TEMP--/entities)--FIX-- Encephalopathy): The combination of PART and LATE-NC significantly increases the risk of dementia compared to either pathology alone
- [Lewy body disease]: Co-occurrence accelerates cognitive decline
- Cerebrovascular disease: Vascular pathology compounds the cognitive effects of PART
- [Argyrophilic grain disease[/diseases/[argyrophilic-grain-disease[/diseases/[argyrophilic-grain-disease[/diseases/[argyrophilic-grain-disease--TEMP--/diseases)--FIX--: Frequently co-occurs with PART in elderly individuals
Studies show that subjects with isolated PART have significantly better overall cognition and slower progression compared to those with comorbid pathologies 3(https://link.springer.com/article/10.1007/s00401-025-02943-x).
PART likely underlies a significant proportion of cases classified as "SNAP" in the biomarker literature — individuals who show:
- Negative amyloid biomarkers: Normal CSF Aβ42 levels, negative amyloid PET scans
- Positive neurodegeneration biomarkers: Elevated CSF total tau and/or [phosphorylated tau], hippocampal atrophy on MRI, temporal hypometabolism on FDG-PET
- Variable tau PET: Current tau PET tracers (e.g., flortaucipir) may have limited sensitivity for the relatively mild tau burden in PART
A major challenge for in vivo diagnosis of PART is that current tau biomarkers] were developed and validated primarily for detecting AD-level tau pathology:
- CSF [p-tau217[/entities/[p-tau217[/entities/[p-tau217[/entities/[p-tau217--TEMP--/entities)--FIX-- and p-tau181 elevations are typically modest in PART and may not reach diagnostic thresholds
- Tau PET signal in PART is generally below reliable detection thresholds for most tracers
- Blood-based biomarkers (plasma [p-tau217[/entities/[p-tau217[/entities/[p-tau217[/entities/[p-tau217--TEMP--/entities)--FIX--, p-tau181) show even lower sensitivity for PART
These limitations mean that PART currently remains a predominantly postmortem diagnosis 3(https://link.springer.com/article/10.1007/s00401-025-02943-x).
¶ Molecular and Genetic Features
The tau pathology in PART is biochemically identical to that in AD:
- Contains both 3R and 4R tau isoforms
- Forms paired helical filaments (PHFs) with the same ultrastructure as AD PHFs
- Exhibits hyperphosphorylation at the same epitopes (AT8, AT100, PHF-1)
- Contains ubiquitinated tau species
This biochemical similarity is a key argument used by those who consider PART to be on a continuum with AD rather than a separate entity.
Unlike AD, PART shows distinctive genetic features:
- **[APOE[/genes/[apoe[/genes/[apoe[/genes/[apoe--TEMP--/genes)--FIX--:139-149.
- Forrest SL, Kril JJ, Wagner S, et al. Primary age-related tauopathy in young adults. Acta Neuropathol. 2020;140(5):671-682. PMID:33147361.## External Links
- [Alzheimer's disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX-- — Related tauopathy with more extensive pathology
- Tau Pathology] — Core mechanism shared with PART
- [hippocampus[/brain-regions/[hippocampus[/brain-regions/[hippocampus[/brain-regions/[hippocampus--TEMP--/brain-regions)--FIX-- — Primary region affected in PART
- [frontotemporal dementia[/diseases/[ftd[/diseases/[ftd[/diseases/[ftd--TEMP--/diseases)--FIX-- — Another tauopathy for differential diagnosis
- [Aging and Neurodegeneration[/mechanisms/[aging-neurodegeneration[/mechanisms/[aging-neurodegeneration[/mechanisms/[aging-neurodegeneration--TEMP--/mechanisms)--FIX-- — Age is the primary driver of PART
The study of Primary Age Related Tauopathy (Part) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
- Crary et al. (2014). Primary age-related tauopathy (PART): a common pathology associated with human aging. Acta Neuropathologica.
- Duyckaerts et al. (2015). PART is part of the Alzheimer's Disease continuum. Acta Neuropathologica.
- Crary et al. (2022). Consensus criteria for the neuropathologic diagnosis of PART. Acta Neuropathologica.
- Jellinger et al. (2015). PART and Alzheimer's Disease: similarities and differences. Acta Neuropathologica.
- Josephs et al. (2017). Tau PET in PART and Alzheimer pathology. Brain.
- Jack et al. (2018). NIA-AA Research Framework: toward a biological definition of Alzheimer's Disease. Alzheimer's & Dementia.
- Braak and Braak (1991). Neuropathological staging of Alzheimer-related changes. Acta Neuropathologica.
- Nelson et al. (2019). Defining and phenotyping PART and related tauopathies. Acta Neuropathologica.
- Robinson et al. (2018). APOE and MAPT relationships in age-related tau pathology. Acta Neuropathologica.
- Jicha et al. (2006). Neuropathologic outcome of mild cognitive impairment following progression to Alzheimer's Disease. Arch Neurol.## External Links
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